1. Field of the Invention
The present invention relates to an oscillator device, such as a crystal oscillator device, and an electronic apparatus, such as a cellular phone, using the oscillator device.
2. Description of the Related Art
A known piezoelectric oscillator device is disclosed in Japanese Utility Model No. 3030652.
FIG. 12 is a circuit diagram of a piezoelectric oscillator device 1 that is substantially the same as the known piezoelectric oscillator device. The oscillator device 1 includes an oscillation circuit 2 and a buffer amplifier circuit 3. The oscillation circuit 2 is a modified grounded-collector Colpitts oscillation circuit and the buffer amplifier circuit 3 is a grounded-base buffer amplifier circuit. An oscillation NPN transistor 2a in the oscillation circuit 2 and a buffer amplifier NPN transistor 3a in the buffer amplifier circuit 3 are connected in series to a power supply. A resistor 4a is connected between the emitter of the transistor 2a and ground. Also, the collector of the transistor 2a is connected to the emitter of the transistor 3a. A resistor 4b is connected between the collector of the transistor 3a and a power terminal 5. The collector of the transistor 3a is connected to an output terminal 7 via a capacitor 6. Accordingly, in the oscillator device 1, a high-frequency component output from the collector of the transistor 2a is input to the emitter of the transistor 3a, is buffer-amplified by the buffer amplifier circuit 3, and is output from the output terminal 7 via the capacitor 6.
In the oscillator device 1, a coupling capacitor is omitted between the oscillation circuit 2 and the buffer amplifier circuit 3, thus reducing the size and cost of the oscillator device.
However, the two resistors 4a and 4b are essential in the oscillator device 1 for the following reasons. Since the resistor 4a functions as an emitter resistance for a load of the oscillation circuit 2, negative resistance is not generated and the oscillation circuit 2 does not oscillate when the resistor 4a is removed. Further, since the resistor 4b functions as a resistance for a load of the buffer amplifier circuit 3, output cannot be taken from the buffer amplifier circuit 3 when the resistor 4b is removed.
Also, in the oscillator device 1, the principal current which flows from the power terminal 5 through the transistors 3a and 2a to the ground causes a voltage drop at the resistors 4b and 4a. As a result, voltages Vce which are applied between the collector and emitter of the transistor 2a, and between the collector and emitter of the transistor 3a are reduced by the voltage drop. These drops in the voltages Vce must be prevented as much as possible because they cause degradation in the amplification factor and power efficiency of the oscillator device 1. Further, many electronic apparatuses require a device which can be operated with a low-voltage power supply, and thus it is difficult to apply a sufficient voltage to the oscillator device 1.
In addition, in the oscillator device 1, the two resistors 4a and 4b consume extra power and occupy extra space, thus increasing the cost of the device.
In order to overcome the above-described problems, preferred embodiments of the present invention provide an oscillator device having fewer electronic components and an electronic apparatus including such a novel oscillator device.
Preferred embodiments of the present invention provide an oscillator device which operates with high efficiency at a low power supply voltage and an electronic apparatus including such a oscillator device.
In the oscillator device according to a preferred embodiment of the present invention, the emitter of an oscillation transistor in an oscillation circuit is directly connected to the emitter of a buffer amplifier transistor in a buffer amplifier circuit or to the source or drain of an FET. The buffer amplifier circuit functions as a load connected to the emitter of the oscillation transistor in the oscillation circuit. Accordingly, a load resistor is not required.
With this unique arrangement, the oscillator device of preferred embodiments of the present invention operates with high efficiency at a low power supply voltage. Further, reduced power consumption, high performance, low cost, and miniaturization are achieved.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.